Gas turbine blades are rotating airfoil shaped components in series of stages designed to convert thermal energy from a combustor into mechanical work of turning a rotor. Performance of a turbine can be enhanced by sealing the outer edge of the blade tip to prevent combustion gases from escaping from the flowpath to the gaps between the blade tip and the outer casing. A common manner of sealing the gap between the blade tips and the turbine casing is through blade tip shrouds.
A feature of a typical turbine blade shroud is a knife edge. Depending upon the size of the blade shroud, one or more knife edges may be utilized. The purpose of the knife edge(s) is to engage honeycomb material located on the inner surface of the outer casing to further minimize any leakage around the blade tip. One typical type of knife edge is shown in U.S. Pat. No. 6,491,498 to Seleski et al.
In some shroud configurations, the knife blade is provided with one or more cutting blades which cut the honeycomb material as the blade rotates. Japanese Patent Publication No. 8-303204 illustrates a knife blade having such cutting blades with one of the cutting blades being at an end of the knife edge and the other being removed from the end of the knife edge.
Often, prior art shrouds having knife edge sealing arrangements suffer from a life shortfall as a result of creep initiated by the extra mass of the cutter feature being located at an outer edge of the shroud. Thus, there is need for an improved shroud construction which meets all sealing requirements, and yet does not suffer from creep which shortens the life of the shroud.